Parashas Masei · Passuk 35:21 · TT note 6
Chabad.org — English translation + Rashi
Torah Temimah points to Sifrei (TT note on “גֹּאֵל הַדָּם יָמִית”).
English: “The blood-avenger shall put to death” — what does this teach? Was it not already said “the blood-avenger, he shall put the murderer to death”? Rather, one might think I have only [the case of] one who has an avenger; from where [do we know about] one who has no avenger? Scripture says “the blood-avenger” — in any case.
Reaffirmation that a court-appointed avenger covers the case of no family avenger.
Even when the victim has no living relative to avenge him, the verse still requires that an avenger (court-appointed) put the murderer to death.